#include <cstdio>

int main( )
{
    __int64 f[ 21 ][ 21 ];
    int i, j, n, m;
    f[ 1 ][ 1 ] = 1;
    for ( i = 2; i <= 20; i++ )
    {
        f[ i ][ 0 ] = 1;
        for ( j = 1; j <= i; j++ )
        {
            if ( j <= i - 1 )    
                f[ i ][ j ] = f[ i - 1 ][ j ] + f[ i ][ j - 1 ];
            else
                f[ i ][ j ] = f[ i ][ j - 1 ];
        }
    }
    while ( scanf("%d%d", &n, &m) != EOF )
        printf("%I64d\n", f[ n ][ m ]);
    return 0;
}
